As is known, dual-mass flywheels are arranged between the internal combustion engine and the gearbox of a motor vehicle and are provided for increasing driving comfort. A dual-mass flywheel of this type is composed substantially of a disk-shaped primary mass which is connected directly to the crankshaft of the internal combustion engine and of a disk-shaped secondary mass which is arranged coaxially with respect to this primary mass and which is connected via a clutch to the input shaft of the gearbox. Here, the two masses are coupled to one another by means of a plurality of damping means arranged between them, said damping means conventionally being in the form of two curved spiral compression springs arranged opposite one another, and this masses can rotate relative to one another counter to the action of this damping means via a friction-reducing bearing arranged on a bearing flange on the primary mass. During operation of the motor vehicle, the primary mass is actively driven by means of the rotating crankshaft of the internal combustion engine, while the secondary mass is carried along by means of the damping elements and in turn drives the gearbox input shaft. Here, the damping elements serve to dampen firstly the non-uniformities resulting from imbalances of the moving masses in the drivetrain, and secondly the rotational non-uniformities of the internal combustion engine resulting from the piston movements.
Since the bearing between the secondary mass and the primary mass of the dual mass flywheel is subjected to particularly high wear in particular as a result of temperature influences from the clutch, this bearing is conventionally formed by special deep groove ball bearings in the form of DFC bearings, such as are known, for example, from DE 42 14 655 A1 and from DE 196 31 725 A1. The deep-groove ball bearings are composed, as is known, of an inner bearing ring and of an outer bearing ring and also of a multiplicity of bearing balls which are arranged between the bearing rings and which roll in groove-like raceways in the outer lateral surface of the inner bearing ring and in the inner lateral surface of the outer bearing ring and which are held at uniform intervals from one another in the circumferential direction by a bearing cage. Since no lubricant replenishment facilities are provided for deep-groove ball bearings in dual-mass flywheels, their service life is therefore dependent on the size of the lubricant reserve provided. To fill the interior space of these deep-groove ball bearings with a lubricant quantity adequate for their entire service life, the bearings therefore have, at one side, special plastic sealing caps which engage over and under the outer bearing ring and the inner bearing ring respectively and which are formed with an additional axial cavity, by means of which the volume of the bearing interior space is increased several times over.
Such plastic sealing caps on the deep-groove ball bearings of dual mass flywheels are however relatively complex to manufacture and are fragile during bearing assembly, and have furthermore proven to be disadvantageous in practice because their seal collar which bears slidingly against the inner lateral surface of the inner bearing ring has a relatively high preload and a relatively low elasticity, as a result of which a high frictional torque acts between it and the inner bearing ring. Here, the high frictional torque is a cause for almost complete premature wear of the seal collar, such that subsequently, as a result of the lack of coverage of the seal region, lubricant leakages occur via the adjoining sealing gap between the plastic sealing cap and the inner bearing ring, resulting in a shortening of the service life of the deep-groove ball bearing.
To avoid the above-described disadvantages, the German patent application with the official file reference 10 2008 048 517.9, which on the filing date of the present application had not yet been published, therefore proposes a rolling bearing for a dual mass flywheel, which rolling bearing has substantially the same design as the deep groove ball bearing described above but is formed with an axial width considerably greater than the standard dimensions in order to attain an interior space volume between the bearing rings which is adequately large to receive a lifetime filling of lubricant. Here, the interior space of the rolling bearing is sealed off by two circular-ring-shaped seals which are situated axially opposite one another and which are formed as metal-reinforced lip sealing rings, which at one side are in each case snapped into a retaining groove in the inner lateral surface of the outer bearing ring and at the other side have in each case two sealing lips which bear slidingly against the outer lateral surface of the inner bearing ring. Furthermore, a plurality of small ventilation bores are formed into the seals at the level of the bearing pitch circle, via which ventilation bores the rolling bearing can be positively ventilated if an admissible gas pressure in the interior space thereof is exceeded, which arises at relatively high temperatures as a result of gasification of the lubricant filling.
However, a disadvantage of the seals for deep groove ball bearings of dual mass flywheels is that the ventilation bores can only be formed by means of complex laser boring, and therefore necessitate the purchase of a correspondingly expensive laser boring device and suitable holding tools. Likewise, laser boring requires additional working steps such as the cleaning of the sealing rings after the lasering of the ventilation bores, and a visual inspection, as a result of which the manufacturing costs of such seals increase toward uneconomical levels. Furthermore, in practice, it has been found that such ventilation bores tend to become blocked as a result of dirt accumulation or gumming of the lubricant, such that the bores can no longer perform the function for which they are intended and, if the admissible gas pressure in the interior space of the bearing is exceeded, the lubricant is forced out via the elastic sealing lips of the sealing rings, likewise leading to a shortening of the service life of the deep groove ball bearing.